Field of the Invention
Aspects of the present invention generally relate to a sheet feeding device, which separates and feeds sheets on a sheet-by-sheet basis from a stack of sheets (a sheet stack) stacked on a sheet storage portion, and an image forming apparatus including the sheet feeding device.
Description of the Related Art
In image forming systems, such as printers, copying machines, and facsimile apparatuses, a sheet feeding device that separates and feeds sheets on a sheet-by-sheet basis from a sheet stack stacked on a sheet storage portion is conventionally known.
Furthermore, due to growing user needs in recent years, demands for performing image formation on sheets of various sizes have been increasing.
Japanese Patent Application Laid-Open No. 10-77123 discusses a sheet feed cassette capable of preventing double feed, non-feed, or other failed feed by ensuring the consistency of leading edge portions in the conveyance direction of stored sheets regardless of sizes of the stored sheets and keeping the press-contact force of a sheet feed roller onto the sheets constant. More specifically, the sheet feed cassette includes a trailing edge guide configured to regulate trailing edges of a stack of stored sheets and having a height of stacking that is variable according to sheet sizes.
However, with regard to the sheet feed cassette discussed in Japanese Patent Application Laid-Open No. 10-77123, although the user performs an operation of adjusting the position of the trailing edge guide so as to regulate the trailing edges of a sheet stack, the position of the trailing edge guide may not be correctly adjusted in some cases.
As one of methods for determining whether the position of the trailing edge guide is correct, there can be conceived a method in which the trailing edge guide is provided with a trailing edge regulation member and a sensor. FIGS. 2A, 2B, and 2C illustrate a specific configuration of a sheet feeding device to which such a method is applied.
The sheet feeding device illustrated in FIGS. 2A, 2B, and 2C is provided with an air separation feeding mechanism that suctions a sheet with air suction by a suction fan, which is located above the sheet stack, and conveys the suctioned sheet. Moreover, the sheet feeding device is also provided with a configuration for determining whether the positional adjustment of the trailing edge guide 504 has been correctly performed (hereinafter referred to as “trailing-edge rough-setting detection”).
In the trailing-edge rough-setting detection, the details of which are described later below, when, for example, a sheet with thicknesses different between leading and trailing edges thereof in the sheet feeding direction, such as an envelope illustrated in FIG. 3, is set in a sheet feeding device, the upper surface of a sheet stack becomes aslant as illustrated in FIG. 2C. If the above-mentioned trailing-edge rough-setting detection is implemented on the sheet stack, the condition of the sheet stack may be erroneously detected.
More specifically, in the sheet feeding device, at the time when a sensor 525 is turned on as a lifter 505 is moved up, the upward movement of the lifter 505 is stopped. In a case where the envelope is set with a flap portion thereof set as the trailing edge side in the sheet feeding direction, the state such as that illustrated in FIG. 2C appears. Therefore, despite the trailing edge guide 504 being correctly set, the upper surface of the sheet stack 501 does not come into contact with a trailing edge detection member 160, and, as a result, a sensor 161 mounted on the trailing edge guide 504 does not come into a detected condition. Accordingly, the sheet feeding device may erroneously determine that the trailing edge guide 504 is not correctly set.
In this way, in a sheet feeding device provided with both the air separation feeding mechanism and the trailing-edge rough-setting detection mechanism, a determination as to whether the positional adjustment of the trailing edge guide has been correctly performed may result in an erroneous detection.